1. Technical Field
The present invention relates to a gain control device in a semiconductor optical amplifier using an optical fiber grating, and more particularly to a gain control device in a semiconductor optical amplifier using an optical fiber grating which uses the optical fiber grating of the semiconductor optical amplifier, which is usually used for a semiconductor optical switching element or a wave converter, to easily control the gain.
2. Description of the Prior Art
A semiconductor optical amplifier directly amplifies an optical signal without any electric conversion. If being constructed in the same structure as a semiconductor laser using compound materials of a semiconductor and making a nonreflecting coating on both sides, the semiconductor optical amplifier may amplify a weak input optical signal.
Because the semiconductor optical amplifier may amplify the optical signal with a high gain through a very wide range of wavelength in a 1.55 xcexcm bandpass optical communication system and has a size much smaller than other optical amplifier, this amplifier can be made in an integrated chip, so spreading its applications like a wave converter or an optical switching and particularly being used as an essential element in an optical cross connect (OXC) system.
However, because an optical signal of a channel corresponding to a certain wavelength varies regardless of other channels in a multi-wave OXC system, strength of all optical signals inputted to the semiconductor optical amplifier as a result varies in a significantly wide range as operation time passes. In this case, the gain in the semiconductor optical amplifier also changes according to the strength of all input optical signals owing to a gain saturation characteristic, which results in jittering an output optical signal. Therefore, a gain of a certain channel is effected by strength of other channels and so unstableness of the gain described above may be deterrent to operate the OXC system.
To solve the problem, there is known a method which employs a phenomenon of making the semiconductor optical amplifier cause oscillation in waves other than a wave of the optical signal using a laser, so varying the oscillated optical strength according to variance of the input optical signal. Using the method, the gain may become stable because the gain of the semiconductor optical amplifier is constant regardless of the strength variance of the input optical signal. For example, a method (Alcatel Gain-clamped SOA) of employing a Pabro-Perot resonator in which the optical fiber gratings are inserted into both input and output terminals of the semiconductor optical amplifier, to oscillate reflective waves of two optical fiber gratings.
However, this method may simplify a structure of the semiconductor optical amplifier but not suggest a technique to control the gain of the amplifier. So, the conventional method has a defect that it may not control the gain easily.
The present invention is designed to solve the problem of the prior art. An object of the invention is to provide a gain control device in a semiconductor optical amplifier using an optical fiber grating, which may easily control the gain of the semiconductor optical amplifier using the optical fiber grating.
In order to accomplish the above object, the present invention provides a gain control device in a semiconductor optical amplifier using an optical fiber grating, which includes an input unit for receiving an optical signal, an output unit for outputting an amplified optical signal, and input and output optical isolators connected to the input and output units to establish paths of the input and output optical signals. The gain control device further includes a tension-controllable optical fiber grating connected to the input optical isolator for fine adjustment of a reflection peak wavelength. A semiconductor optical amplifier connected to the tension-controllable optical fiber grating is also provided to amplify the optical signal. A power supply supplies power to the semiconductor optical amplifier to drive the optical amplifier. In addition, an optical fiber grating is connected to the semiconductor optical amplifier and has a predetermined reflection peak wavelength.